DTA

Dottorato

MODESTI, MARGHERITA

etd-03232021-171722

Effect of pre- and post-harvest treatments with ozone on grapes berry physiology and wine quality parameters

AGR/03

Istituto di Scienze della Vita - AGROBIOSCIENCES

relatore Prof. TONUTTI, PIETRO

• Vitis vinifera
• stomatal conductance
• gene expression
• pathogen control
• oxidative stress
• NIR
• Wine grapes
• VOCs
• polyphenols
• sulphur dioxide
• amelioration
• glycoconjugates
• rate-all-that-apply
• smoke taint
• volatile phenols
• smoke taint
• bushfires
• sangiovese

11/05/2021;

parziale

European Community imposed a considerable restriction of the use of pesticides establishing a regulatory framework for the sustainable use of agro-chemicals. Considering the huge use of pesticides used for wine production, the environmental impact of viticulture sector is growing day by day. In addition to the environmental issues, consumers are increasingly oriented towards the purchase of safer food and beverage, which is pushing the wine sector to strongly reduce the use of chemicals both in vineyards and wineries. Alternative protocols must be on one hand efficient, economically affordable, and easy to use but also harmless for the environment and human health. Another emergency is represented by the climate change due to the increase of greenhouse gases. One of the consequence is the general increase of temperature and the more frequent hot and dry summers resulting, in specific world areas, in extensive bushfires. In these areas, wine producers are dealing with a related new phenomenon called “smoke taint” of wine. Hence, when fires occur in proximity of vine growing areas grapes are exposed to smoke. This exposure leads to a range of changes in the chemical composition and sensory characteristic leading to wines characterized by smoky, ashy, and medicinal flavor. This PhD thesis aimed to clarify the effects of different pre and postharvest ozone application to reduce the use of chemicals in the wine production chain. Additionally, the possibility to use ozone on smoke affected grapes to reduce the smoke taint in wine has been evaluated. Ozone is a strong oxidative gas, which decomposes spontaneously and that is employed in an increasing number of wineries as a sanitizing agent, allowing sulphur-free wine production (Purovino®, PC Engineering, Uggiate Trevano, Italy). Due to its oxidative potential, it represents a valid alternative to the use of sulphur-dioxide during the winemaking and could potentially reduce the smoke taint of the wines. On the other hand, much less is known on the effect of ozone on vines. The thesis also aimed to investigate how the ozone treatments affect the aromatic profile of grapes and wine. Using different analyses and statistical approaches, it also aimed to gain insights into modifications in vines physiological state and grape composition caused by different ozone application. A metabolomic- and molecular-based approach has been used to identify molecular markers of ozone exposition. Pre-harvest treatments have been performed spraying the whole canopies of Vitis vinifera (cv Sangiovese) with ozonated water throughout the vegetative growth during 2018 and 2019 growing season. Additionally, gaseous ozone treatments have been performed on potted plants for two consecutive growing seasons. Post-harvest treatments have been carried out on bunches of wine grapes cv Sangiovese exposed to gaseous ozone for 12 hours at 10 °C. The trials were performed for three consecutive years (2017, 2018 and 2019). Lastly, wine grapes Cabernet Sauvignon and Merlot smoke-affected grapes were treated with gaseous ozone for 12 and 24 hours in two consecutive vintages (2019 and 2020). Leaves collected from the open field experiment and on potted vines were analysed to assess the effects of ozone treatments in inducing the expression of systemic acquired resistance (SAR) related genes. Furthermore, physiological and structural changes have been analysed to monitor possible stress-related responses. Grape berries treated with gaseous ozone in post-harvest were analysed to evaluate how the treatments affect berry composition, especially regarding volatile and polyphenols accumulation and biosynthesis. Sensory traits and aromatic composition of wines made from the trials have been assessed. Lastly, the concentrations of smoke taint marker compounds, responsible for the smoke taint have been analysed in grapes and wines through analytical and sensory approaches. Ozone induces a temporary up regulation of specific SAR-related genes (chitinases, β-1,3-glucanase and glutathione-S-transferase). Pathogen-related (PR) genes showed a more persistent over expression. Ozone treatment affected stomatal conductance but differentially according to different ozone doses. NIR spectrum analyses revealed important structural changes in ozone treated plants, especially in leaves exposed to higher doses of ozone. Post-harvest ozone treatment increased total polyphenols and total flavonoids, and specific genes (PAL, FLS involved in polyphenols biosynthesis were up-regulated. Furthermore, ozone fumigation slightly affected the aromatic profile of grapes and wine, especially considering specific aroma compounds derived from the lipoxygenase pathway. Lastly, high amount of volatile and glycosylated phenols was observed in smoked grapes and wines. The amount of these compounds was significantly lower in smoke-affected and ozone-treated grapes and in the resulting wine. This wine also showed a less intense smoke-related sensory attributes. Based on these results, ozone application can be considered a promising substitute to the use of chemicals in viticulture, also thanks to the induction of resistance-related genes expression. Ozone post-harvest application induces limited changes in grape composition and wine aroma, and it can be safely used to avoid the use of sulphur dioxide. Lastly post-harvest ozone treatment on smoke affected grapes seems to be effective in mitigate the smoke taint in wines.

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